GNU Ada

GNAT (formerly the GNU NYU Ada Translator) is a full Ada compiler and runtime library supporting Ada 2005, Ada 95, and Ada 83. It is a full implementation of the language, including all of the optional Annexes of the Language Reference Manual. It is based on GCC technology, and has source, pre-packaged releases, and several additional Ada tools available. The runtime has a modified GPL so that your applications don't have to be GPLed automatically.